Active transport

Active transport moves particles across a cell membrane from a region where their concentration is lower to a region where their concentration is higher.

This movement is against the concentration gradient: particles move towards the region where there are already more of them. Membrane proteins transport the particles across the membrane using energy supplied by respiration.

Mineral ion uptake by root hair cells

Root hair cells take up mineral ions dissolved in the water around soil particles, known as the soil solution. The ions enter through the root hair cells’ cell membranes.

The concentration of a mineral ion may be lower in the soil solution than inside a root hair cell. In that case, uptake moves the ion from a lower concentration to a higher concentration, against its concentration gradient. The cell achieves this by active transport.

During active transport, carrier proteins in the cell membrane move ions into the cell using energy supplied by respiration. This allows roots to obtain mineral ions needed by the plant even when the ions would not move into the cells down their concentration gradients.